A. Conjugated linoleic acid (CLA), found naturally in meat and milk, is a polyunsaturated fatty acid that's growing in popularity as a dietary supplement. Some supplement manufacturers make exuberant claims that CLA can help you lose weight, build muscle, and even fight diseases such as cancer and diabetes. However, the scientific evidence on this fatty acid is not so clear cut.

Here are some current areas of CLA research:

1. Body fat. Some studies have found that CLA supplementation can reduce body fat in overweight people, while other studies have found no improvement in body composition. A 2012 study published in Nutrition found that among 80 overweight and obese Chinese subjects, two daily doses of CLA (1.7 grams each) for 12 weeks reduced body fat by 2 percent, though cholesterol levels worsened slightly.

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2. Heart disease. Some research supports that CLA can reduce the development of atherosclerosis--the formation of plaque in the arteries that leads to heart disease--by lowering levels of blood lipids, but a 2010 clinical trial did not find any anti-atherosclerotic effects from CLA treatment in overweight or obese participants.

3. Cancer. In test tube and animal studies, CLA seems to inhibit cancer cells, and high dietary CLA intake has been linked with lower risk of colorectal and breast cancer in women, but these results are preliminary.

4. Diabetes. CLA may improve fasting blood glucose, because of such factors as improvement in the body's response to insulin, body composition, and levels of the hormone leptin, which can influence appetite. But some studies have found that some forms of CLA supplements may worsen blood glucose control.

5. CLA and bone health. High dietary intake of CLA has been linked with improved bone mass, due to decreased fat levels in the body, but the research has been inconsistent in this area, possibly due to various levels of calcium intake.

THE BOTTOM LINE
There are more questions than answers over the impact of CLA on health. In fact, a 2011 review examining the evidence on CLA published in Nutrition Research Reviews concluded that almost all of the promising research has been in animal and test tube models; of human studies the only evidence that is broadly consistent is CLA's modest effect on body fat.

Several safety concerns have arisen, including possible pro-diabetic effects, increased size of liver and spleen, gastrointestinal upset, and altered nutritional value of breast milk in lactating women. For now, our best advice is to consume CLA as a part of your diet in meat and dairy products, but think twice about taking supplements. If you still feel a need to take them, first consult your health care provider to discuss whether they offer benefits for you.